Here are a few internet resources to help you find information about the 300-plus BSA local councils.
Dave Hultberg is a Pennsylvania scouter who has put together an Excel spreadsheet listing all current and former BSA councils. It has the dates the council has been (or was) in existence as well as the current council web address. Link (Excel file)
The BSA National website has a Local Council Locator that permits you to find any council by zip code or by council number. Link
The National website also has a Local Council Websites page providing council website addresses. Link
And at the Locations of BSA Councils page on the U.S. Scouting Service Project site is the map shown above indicating the location of every BSA council headquarters (as of 1995). Link